derail

A device placed on railway tracks causing a train to derail.

“The derail was placed deliberately so that the train would fall into the river.”

An instance of diverting a conversation or debate from its original topic.

To cause to come off the tracks.

“The train was destroyed when it was derailed by the penny.”

To come off the tracks.

To deviate from the previous course or direction.

“The conversation derailed once James brought up politics.”

To cause to deviate from a set course or direction; derange.

“The protesting students derailed the professor's lecture.”